Lymphomas comprise a complex set of diseases, each tumor the product of clonal neoplastic expansion of cells belonging to a particular lymphoid subpopulation at a discrete stage of differentiation. In high-leukemia strains of mice, onset of leukemia is accompanied by the appearance of recombinant virus thought to be the leukemogenic agent. The goal of this work is to determine the relevance of expression of recombinant murine leukemia virus antigens to X-ray lymphomagenesis in mice. The phenotypic diversity and stability of primary lymphomas will be determined by quantitative microfluorometric analysis, using monoclonal antibodies to lymphocyte differentiation antigens. Tumors will be examined for cell surface expression of antigens related to murine leukemia virus. Specific viral probes and restriction endonuclease will be used to detect recombinant murine leukemia virus sequences in DNA of tumor cells. Monoclonal antibodies will be constructed and used to detect tumor-associated antigens, including clonally expressed antigens, and to examine the possible role of these as viral antigen receptors.